This invention relates to a vehicle transmission having a gearshift range preconditioning system, which can be particularly advantageous in vehicles with a need for quick shifting time and mantaining shifting accuracy.
In vehicles having typical power-assisted semiautomatic or fully automatic transmission for conventional synchromesh-type transmissions, there are several neutral positions. To facilitate automatic gear selections in such transmissions, one neutral selection system and one active gear selection system are provided. During a gear-change operation, these two systems are shifted in a prescribed sequence and in such a way that any one gear allows the immediate selection of any other gear.
Presently known gearshift conditioning arrangements typically include an electronic logic portion which prohibits the selection of a specific gear only if an inadmissible rate of engine revolutions were existent. One gearshift control arrangement, which provides for a conditioning of the gearshift lever depending on similar vehicle performance criteria, can be found in the U.S. patent application Ser. No. 348,038, which is assigned to the assignee of the present invention and which has matured into U.S. Pat. No. 4,507,736.
This system, however, is directed more toward an inline-type gear-selecting arrangement, which does not have a plurality of neutral range positions generally associated with a H-type gearshift arrangement. To accomplish the actual shifting operation, the vehicle transmission system typically includes fluid-pressure-actuated operating cylinders which assist in shifting to a neutral position from any gear, and from a neutral position to any gear. In the case of a neutral selection being initiated through a transmitter, which is controlled by the vehicle operator, it is not determinable to which neutral range within the transmission that the actually-engaged neutral gear is assigned; this range possibly could be between the lower gears, the higher gears, or even adjacent the reverse gear. Normally, the cylinder controlling the neutral position operates such that the neutral gear remains in the neutral range nearest the previously-selected active gear. This arrangement has the disadvantage that, now, if starting from a certain neutral position of the transmission, a gear selected which is not within the same neutral range in which the neutral position had been situated, then the new neutral range must first be selected. Under certain driving conditions, this creates a delay resulting in the total shifting time of the transmission. If, for instance, the vehicle is started from a standstill position, and if the engaged neutral range happens to not be situated adjacent the active gear used for starting the vehicle, a first neutral range change must occur. The same rule applies when a vehicle operator (while the vehicle is moving) shifts first only into the neutral range, and then allows the vehicle to roll for a distance before shifting into the necessary active gear; in this instance, a first neutral range shift must also occur.
Such undetermined selection of passive neutral ranges may additionally entail a safety risk with respect to the accuracy of the shifting operation. In the previously-described instance of the vehicle rolling while in an undetermined neutral range, access to the reverse gear may be inadvertently achieved with equipment damage resulting therefrom.